Auxins are an important family of plant hormones that influence various aspects of plant growth and development. Indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) are two endogenous auxins involved in root elongation inhibition and lateral root induction. It has been proposed that IBA has two mechanisms of action in vivo: via its conversion to IAA through f3-oxidation in the peroxisomes and/or a relatively unknown process via its own activity independent from IAA. Mutants resistant to IBA and sensitive to IAA, termed IBA-response mutants, will be isolated and characterized to examine these modes of action. They will be divided into two general groups, those with defects in f3-oxidation and those with defects outside of n-oxidation. The first group of mutants is currently being characterized and appears to confirm IBA is converted to IAA. The second group of mutants may elucidate the action of IBA independent from IAA. ibr6 is one such mutant that appears to be defective in IBA transport as seen by its resistance to auxin transport inhibitors. The identification and characterization of the gene defective in this mutant will allow me to elucidate this second mechanism of IBA action.